1. Technical Field
The present invention relates to an ink-circulation type inkjet printing device.
2. Related Art
There are known ink-circulation type inkjet printing devices that eject ink from an inkjet head while circulating the ink, thereby performing printing.
One of the ink-circulation type inkjet printing devices is a device that applies positive pressure and negative pressure to a pressure tank disposed on the upstream side of the inkjet head and a negative pressure tank disposed on the downstream side thereof, respectively, thereby circulating the ink (see, for example, Patent Document 1).
The inkjet printing device described above uses an air pump to apply positive pressure and negative pressure to the pressure tank and the negative pressure tank, respectively, when performing printing. With this configuration, the ink flows from the pressure tank to the inkjet head. The ink that has not been consumed in the inkjet head is collected in the negative pressure tank. Then, the ink is fed from the negative pressure tank to the pressure tank with an ink pump. As described above, the ink is circulated.
Incidentally, in the inkjet printing device, the ink remaining in the nozzles of the inkjet head may be thickened during standby. This thickened ink may cause troubles in ink ejection such as disturbance of directions of ink ejected from nozzles and failure to eject ink. Furthermore, foreign substances such as dusts may be attached to the nozzles to cause another trouble in ink ejection.
To address these troubles, the inkjet printing device performs so-called purging of supplying pressurized ink from an ink supply source to the inkjet head to forcibly discharge the ink from the nozzles. Through the purging, thickened ink and the like are pushed out from the nozzles, thereby preventing the ejection troubles.
The pressure within the pressure tank is increased in the case where the purging is performed in the ink-circulation type inkjet printing device described above. With this configuration, the ink is supplied from the pressure tank to the inkjet head and the ink is forcibly discharged from the nozzles.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2012-153004